Carboxyl group-containing polymers represented by sodium poly(meth)acrylate and the like are widely used for applications such as detergent builders, pigment dispersants (dispersants for inorganic particles), chemicals for water treatment (scale inhibitors). Polymers having better properties are demanded in the markets of these applications.
In order to meet the demand, Patent Literature 1, for example, discloses a polymer with a pH maintained at 4 or higher which is obtained by reacting 100 parts by weight of a polymer of α,β-monoethylenic unsaturated carboxylic acid with 1 to 70 parts by weight of a compound containing a metal such as calcium. Patent Literature 2, for example, discloses a method of producing a water-soluble polymer obtained by continuously adding a chain transfer agent during a predetermined period in the polymerization period, where the addition rate of the chain transfer agent to the monomers is changed at least once. Patent Literature 3, for example, discloses a method of producing a low-molecular weight (meth)acrylic acid (salt)-based polymer. The method includes polymerizing a monomer component including monomers such as a monoethylenic unsaturated monomer of a monocarboxylic acid (salt) in a highly concentrated aqueous solution in the presence of an alkali substance, using a polymerization catalyst. In the method, the polymerization catalyst is a combination of persulfate and hydrogen peroxide, and the total amount of the alkali substance is 99 mol % or lower of the amount required to neutralize the whole acid groups of the monomer component. Also, the dropping of the hydrogen peroxide is set to be ended more than ten minutes before the end of dropping the monomer component.
Patent Literature 4, for example, discloses a grinding agent including acrylic acid polymers and/or copolymers. The grinding agent is for an aqueous suspension of coarse mineral particles for pigments, and includes the polymers and/or copolymers which are partially neutralized by at least one neutralizing agent having at least one monovalent functional group. Patent Literature 5, for example, discloses a method of producing a dispersion of mineral particles suitable for use as pigments. The method includes the steps of: (A) preparing a mixture comprising water and a mineral to be ground, comprising particles and the mixture having at least 75% by weight of solids content, based on the total weight of the mixture; (B) introducing a fully neutralized dispersing agent into the mixture, in an amount of from 0.1% to 0.5% by weight, based on the dry weight of the mineral present in the mixture; (C) grinding the mixture to produce an aqueous dispersion; (D) introducing at least two portions of a partially neutralized dispersing agent, which has been at least 30% neutralized, based on equivalents of acid groups into the dispersion during grinding, wherein the total of the portions is from 0.2 to 1.0% by weight, based on the dry weight of the mineral present in the mixture; and (E) continuing grinding the dispersion until 95% or more of the mineral particles have a maximum particle size below 2 microns.